Automated media preparators may be valuable in both large and small food testing labs. In using a media preparator in a large lab, with an incubator room, the lab manager first determines the approximate daily sample volume and the amount of enrichment media that would be required in total using traditional testing methods. Sterilized water is then pre-dispensed into test containers to which the concentrated enrichment media will later be added. These sterilized water containers are placed into the incubator room to maintain the proper test temperature prior to testing. When using the system in a smaller lab, without an incubator room, the media preparator is adjusted to dispense directly into the test container, just above the target test temperature, and concentrated QC approved enrichment media is added to the sterile heated water containers. This allows the enrichment media and the sample to maintain the proper temperature prior to and during incubation.
The following example outlines the testing economies that can be realized by using an automated media preparator. Using traditional media preparation methods, a lab receiving 40 test samples per day at 375-gram sample size each would require 3375 mL of heated enrichment media per sample, or 135 liters of enrichment media per day. By using an automated media preparation system, only 20 liters of concentrated media would be required each day, nearly an 85 percent reduction in volume. This concentrated enrichment media is then added to the remaining volume of sterile water—dispensed at predetermined temperature by the media preparator.
The reduction in costs associated with autoclave use to heat enrichment media in this manner is dramatic, as outlined in Table 1. In the standard procedure, 14 hours of autoclave time is required each day to heat the 135 liters of enrichment media, at a cost of about $245 in labor (14 hours x $17.50-hour labor cost). Using concentrated media and a media preparator, only four hours of labor would be required each day: two hours to make the 20 liters of concentrated sterilized enrichment media, and two hours to dispense 115 liters of pre-heated and sterilized test water. The daily cost savings would be $175; 10 fewer hours of labor; and 12 fewer loads in the autoclave.
The savings add up. In the example described above, the weekly labor cost savings comes to $1,225, or over $63k a year. Obviously, the larger the volume of media required each day for testing, the greater the cost savings, and the faster the automated media preparator will pay for itself. In addition to the number of hours required to prepare 135 liters of enriched media per day, the autoclaves in themselves are huge limiting factors in terms of production throughput in the testing lab. Smaller autoclaves aren’t capable of keeping up with the large volumes of enrichment media that may be required, and large autoclaves can easily cost more that the media preparation system itself and can require additional staff to keep up with the sample volume.
As an example of a media preparatory, the Demeter, manufactured by Heateflex Corp. (see image), automatically heats and dispenses sterile water at a pre-determined temperature into a test container, to which sterile concentrated enrichment media and the test sample is then added. The dispense is highly precise and accurate for each test, eliminating human error. Onboard electronics provide traceability for test temperature and volume, and up to 16 pre-programmed test recipes/dispenses are available for various volumes (225 mL to 5000 mL) and test temperatures (0 to 50 degrees Celsius). An ultraviolet light filtration system ensures that the test water is sterilized prior to the dispense. For recordkeeping, the system includes a scanner to record sample and batch data, and a barcode label printer for affixing test information to the sample container.